This invention relates to a double-cylinder circular knitting machine with latch needles and automatic needle latch opening, i.e. having the needle latches that open automatically before the needles pick up the yarn or thread to be knitted.
More specifically, the invention concerns such a machine capable of carrying out all of the knitting operations commonly carried out on a double-cylinder machine, but having a simpler construction.
A double-cylinder machine is known to be of rather complex construction, and in particular to include a large number of cams for driving the jacks and sliders, part of such cams being movable, i.e. displaceable to two positions differently spaced apart from the needle cylinders such as to only act on the butts of pre-determined sliders or jacks. These movable cams require for their displacement the arrangement of levers or other members around the machine, which complicates the machine design and increases the bulk thereof, since all such levers must derive their motion from the machine programming drum.
Also known is that the cams may induce considerable stresses on the sliders and/or needles, or parts thereof. In particular, it is known that the so-called latchguard cams, mainly provided to hold open the latches of the rib needles operating in the upper needle cylinder, can generate considerable stress in the latches of such needles, which stress becomes higher the narrower is the loop on the needle, since that loop is arranged between the open latch and the needle stem, and lever acts on the latch, which is thus pressed against the latchguard cams.
The latches of the rib needles, moreover, may strike the sloping flanks of the latchguard cams at a more or less open position during the movement of such needles to a floating or neutral position, that is a raised non-knitting position. If a latch is too open, it may happen that the impact on the sloping flank of the latchguard cam, rather than causing the latch to open, bends it, thereby the latch damages and the yarn is no longer allowed to run freely along the latch.
Quite often, during the return stroke of the reciprocating motion in forming the heel of a stocking or sock article, the latches of the needles operating in the lower cylinder are also forced against the lower portion of the latchguard cams.
Those same latchguard cams are also difficult to manufacture and require the availability of skilled labor. Furthermore, they involve considerable waste of material, since they must be made from a single ring, although they only occupy peripherally but part of the cam box circumference.
The various stresses induced in the needles and sliders of a double-cylinder machine also include those caused by the slider pushing cams, so termed because they push the sliders against the bottom of the respective grooves when the needles and sliders cross one another to open the needle latches, which slider pushing cams transmit shocks to the sliders and needles, as these move at a high speed past them.